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Date:      Mon, 6 Dec 1999 09:58:59 -0800 (PST)
From:      Matthew Jacob <mjacob@feral.com>
To:        Mike Smith <msmith@freebsd.org>
Cc:        hackers@freebsd.org
Subject:   Re: tty level buffer overflows 
Message-ID:  <Pine.BSF.4.05.9912060956510.3258-100000@semuta.feral.com>
In-Reply-To: <199912060441.UAA00805@mass.cdrom.com>

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> > 
> > > Er, you should read the sio(4) manpage too.  tty-level buffer overflows 
> > > have nothing to do with interrupt latency/execution time.
> > 
> > You mean this:
> > 
> >      sio%d: tty-level buffer overflow.  Problem in the application.  Input has
> >      arrived faster than the given module could process it and some has been
> >      lost.
> 
> Yup. Ignore the "problem in the application" part, as that predicates 
> that the kernel and driver are working properly, which doesn't seem to be 
> the case.  The problem here is that the buffer between the top side of 
> the driver and the application isn't being drained fast enough.  It would 
> be educational to know what the app is sleeping on when these messages 
> are emitted; just dropping to ddb and using 'ps' would probably be 
> enough.  There has to be some reason that the process is either not being 
> woken when data arrives, or is being held up somewhere else for long 
> enough that the clist overflows.

That's tough because it's transitory and hard to notice as I only rlogin
into this machine! Sounds to me a gdb breakpoint is what's needed, but
this is difficult to do for this machine.

> Does the problem still manifest with the recent scheduler changes?  
> Perhaps the comms processes are being unfairly scheduled against for some 
> reason?

The kernel is a November 12 kernel. Maybe it's better now. However, I'm
still staggering under the recent bdev changes - when everything has
settled down and all my other freebsd machines can boot all the way up and
are all up to date, I'll revisit this.





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